A passive optical network (PON) is a network architecture employing fiber cables to connect a central office to local premises. It employs passive optical components to enable optical feeder fiber to serve multiple premises. A PON consists of one or more central office (CO) nodes, where the optical line terminal (OLT) equipment is located, one or more termination nodes at customer premises, called optical network terminations (ONT) or optical network units (ONU) and further infrastructure such as optical fiber, power splitters (PSs), filters, etc. which connect the central office node to the termination nodes. This infrastructure is called the optical distribution network (ODN). In other words, the ODN provides the optical transmission medium from the OLT towards the ONUs and vice versa.
A passive optical network may operate over multiple wavelengths in a wavelength-division multiplexing (WDM) scheme. An example of such network is the standardized Gigabit passive optical network (NGPON2) operating over 4 wavelengths in TWDM-PON scheme. A TWDM-PON is a multiple wavelength PON solution in which each wavelength is shared between multiple optical network units by employing time division multiplexing and multiple access mechanisms.
The case where the owner of the fiber infrastructure of the optical distribution network is different from the operator of the active network equipment (such as the optical line termination) occurs more and more in today's utilization of passive optical networks. FIG. 1 shows an architectural diagram of a PON implementation where in the central office location a network provider operates active network equipment consisting of four different OLTs operating at four different wavelengths λ1-λ4 multiplexed to one fiber. The optical distribution network constitutes the domain of fiber infrastructure and is managed by an infrastructure provider who can be different from the network provider.
For such a setup it is possible to deploy unbundling of the access network at the physical level, for instance due to regulation needs. The type of physical unbundling being typically considered for this case is the “wavelength per service provider”. This can provide the best level of isolation of network providers operating over the same optical fiber but on different wavelengths. Such a scenario of physical unbundling with the “wavelength per service provider” scheme with 4 network providers (NPs) is illustrated in FIG. 2. The figure illustrates the case where not all NPs with their associated wavelength are located at the same Central Office (CO) location. Each NP has its own OLT as shown in FIG. 2 as OLT1, OLT2, OLT3 and OLT4. Each OLT operates on a different wavelength, i.e. each OLT sends and receives signals of a different wavelength.
In the case of unbundled optical infrastructure, each of the wavelength planes is operated separately and must not be necessarily located at the same CO location. Each OLT and ONU must operate at the upstream (US) and downstream (DS) wavelength designated for that network operator so that the traffic between them does not collide with traffic from other operators transported over the same optical infrastructure. With the term uplink or upstream we refer to signals travelling from the ONUs to the OLT. With the term downlink or downstream we refer to signals travelling from the OLT to the ONUs. Furthermore a security issue may occur in the case that an ONU or OLT becomes able to receive signals originating from network providers other than its own network provider.
Reference has been made until now to OLT and ONT since we refer to the passive optical network (PON) system. The unbundling scenario can also be applicable to the case of co-existence of PON with other optical systems, such as a common public radio interface (CPRI) optical system.
In the case where not all OLTs are located at the same CO location there is a risk that DS traffic originating from e.g. OLT4 when transmitting on the wrong wavelength is creating collision with DS traffic of any other NP on the same distribution network.
Furthermore the physical unbundling may increase the dynamicity in the system (as well as in the ODN) as customers might change their NP and related services more frequently or even receive traffic from multiple NPs in parallel. In these cases the ONUs would be required to change the allocated wavelength of a respective NP or be able to receive optical signals of multiple wavelengths. This would require the ODN to be enhanced in a way which would enable the connection of any ONU to any required OLT and vice versa.
In a WDM PON system it is today assumed that all NPs are fed into the ODN from the same CO location. In a physically unbundled solution, as shown in FIG. 2, a network provider having OLT4 might want to use the ODN (when several network providers share the ODN through physical unbundling) from a different location than the ones of OLT1, OLT2 and OLT3. This case is not yet covered by any existing solution.